The present invention relates generally to radio-frequency conductors and more specifically to an RF multi-layer clad coaxial cable.
Coaxial cables and other radio frequency (RF) cables are known in the art for transmitting high frequency signals. Known conventional coaxial cables are typically formed from an inner tube of conducting metal, a dielectric material surrounding the inner tube, and an outer tube of conducting metal. The conductors may be tubular or solid. The two tubes formed of metal or other electrically conductive material are disposed concentrically with the dielectric material disposed between the two tubes. The conductivity of the material used to form the tubes, and the relative permittivity and dissipation factor of the dielectric material determines the RF attenuation of the resulting coaxial cable.
As is known in the art, at radio frequencies the current flowing through the conductive tubes of the cable tends to flow only in and directly beneath the surfaces of the conducting tubes. This is commonly known as the xe2x80x9cskin effect.xe2x80x9d More particularly, current flows through and directly beneath an inside surface of the outer tube and an outside surface of the inner tube.
Each tube may be typically manufactured by bending a flat strip of conductive material or other thin metal into a round tube and welding the longitudinal edges of the material together to form a seam. To minimize manufacturing costs, the material selected for forming the tubes is preferably one that is easy to form and weld. However, the materials that provide the best cost benefit do not necessarily offer the preferred RF electrical conductivity.
Additionally, materials such as copper provide excellent electrical characteristics, but are relatively expensive. To reduce manufacturing costs, it is known to form the conductive tubes of cladding material or layers of different metal to minimize the use of relatively costly material. For example, it is known to form the conductive tubing from copper and aluminum layers. However, the copper-aluminum boundary presents difficulty when welded.
U.S. Pat. No. 6,342,677 B1 assigned to Trilogy Communications, Inc. discloses a high frequency cable made of clad material. In this cable, a base layer of low conductivity material extends past the longitudinal edges of a layer of high conductivity material. When the strip is formed into a tube, xe2x80x9cclearancexe2x80x9d edges formed of the low conductivity material are welded. However, such low conductivity material may be more difficult to weld than the high conductivity material. The presence of low conductivity materials in the RF path to degradation of the electrical properties, which is undesirable.
Accordingly, there is a need for a coaxial cable that has high conductivity to minimize RF attenuation, is relatively economical to manufacture by minimizing use of expensive metals, yet is easy to manufacture and weld.